Fuel channel fasteners have been used for many years in boiling water reactor fuel assemblies. The purpose of the fastener is to mechanically attach the external fuel channel to the fuel assembly, so that under operating conditions, the reactor coolant is restrained around each fuel assembly. The fastener utilizes a spring to separate the fuel channel from other fuel assemblies in the proximity of the fuel channel. The current designs of fuel channel fasteners, therefore, provide a solid stop between adjacent channels.
Previous fuel channel fastener designs have several significant shortcomings. The bolt in these designs was moved toward a more inward position, as compared to the exterior edge of the fuel channel. The placement of the bolt in this arrangement provided a tendency for the entire fastener to rotate during tightening of the bolt. As manufacturers have modified the bolt position of fuel channel fasteners from a position close to the edge of the fuel channel further toward an inside part of the fuel assembly, the additional distance from the bolt to the external parts of the fastener decreases the rotational resistance due to the additional moment arm.
The rotation of the bolt caused the body of the fastener to rotate on the fuel assembly channel, thus allowing the bottom edge of the fastener body to protrude from the exterior of the channel wall. This rotation thereby allows an additional contact edge which may lead to premature failure of the fuel channel fastener as there is an additional contact surface for impact. The rotation also allows the end of the fuel channel spring to extend beyond the protective configuration of the body of the fastener. When the fastener body or spring extends outward, they are more likely to be damaged by interacting with in-reactor blade guides, fuel storage racks, other fasteners, or reactor components during, for example, fuel assembly movement. Industry experience has shown that fuel channel fasteners can prematurely fail using these designs.
There is a need to provide a fuel channel fastener that will allow for adequate seating of the fuel channel fastener to the fuel assembly.
There is also a need to provide a fuel channel fastener that will be rugged for anticipated operating and accident conditions for a nuclear reactor.
There is a still further need to provide a fuel channel fastener that will be less susceptible to damage compared to current fuel channel fastener designs.